1. Field of the Invention
The present invention relates to a cooling structure of a motor-assist device for a vehicle, in which a motor control device (inverter) connected to a motor of the motor-assist device for driving a vehicle is cooled by a cooling system separate from the cooling system of the motor-assist device.
2. Description of the Related Art
Recently, hybrid cars have been developed in order to avoid environmental pollution due to exhaust gases. These cars have an engine and a motor/generator, and both or either of which is actuated to drive the vehicle as needed.
The above motor/generator functions as a generator by subjecting a driving shaft of the motor to a torque applied from the wheels and the generated power is stored in a battery via an inverter during braking of the vehicle. On the other hand, during driving of the vehicle, the electric power in the battery is converted to three-phase AC power by the inverter. The AC power is supplied to the motor/generator, so that the motor/generator functions as a motor and is actuated to drive the vehicle.
The motor/generator is interposed between the engine and the transmission which are mounted in the front of the vehicle. The inverter for converting direct current into alternating current, which is connected to the motor/generator, is mounted in the rear of the vehicle when there is no mounting space in the front of the vehicle. Since the inverter generates heat due to the flow of current, the inverter is provided with a cooling system for facilitating the heat radiation.
The conventional cooling system of the inverter is provided with an inverter-cooling pipe in which a cooling path in the engine mounted in the front of the vehicle branches off from a heat exchanger to the inverter and circulates therethrough. The cooling pipe has a water pump interposed therein and is filled with a cooling liquid such as water. The cooling liquid is allowed to circulate by actuating the water pump and the heat radiates from the heat exchanger (disclosed in Japanese Patent Laid-open No. Sho 62-255266).
In the above-described conventional art, when cooling water of the engine is used to cool the inverter, there is a problem such that the cooling pipe in the inverter-cooling system becomes long depending on the position at which the inverter is mounted. Also, it is difficult to control the temperature of the water, which is required by the inverter, due to the temperature of the engine.
Furthermore, when the cooling water of the engine and the cooling liquid of the inverter are allowed to flow through a different cooling path, arrangement of parts, such as the pump for circulating the cooling liquid, the radiator for facilitating the heat radiation, and a cooling pipe, in the vehicle may be difficult because of the constraints of the parts of a rear-wheel drive and suspension system and an exhaust system.
The present invention is made in consideration of the above problems. Accordingly, it is an object of the present invention to provide a cooling structure of a motor-assist device for a vehicle in which a second cooling system for cooling a motor control device, which is separate from an engine-cooling system, is provided so as to shorten a cooling pipe, and in which a radiator is disposed inside a rear bumper, thereby circumventing constraints in the arrangement of the cooling parts and facilitating control of the water temperature.
In order to achieve the above object, according to the present invention, there is provided a cooling structure of a motor-assist device for a vehicle in which a motor housing including a motor connected to a motor control device is disposed between an engine and a transmission which are mounted in the vehicle, and in which the motor-assist device for the vehicle is cooled by a first cooling system,
wherein the first cooling system for cooling the motor-assist device for the vehicle is formed in such a manner that a cooling path is formed in the motor housing, an inlet of the cooling path is connected with a heat exchanger, and a heat exchanger and a water pump driven by the engine are connected with each other, and wherein the motor control device is mounted in the rear of the vehicle and a second cooling system for cooling the motor control device is provided separately from the first cooling system.
According to the present invention, the second cooling system which is separate from the first cooling system (assist-cooling system) is provided to cool the motor control device mounted in the rear of the vehicle, and the size of the second cooling system can be determined based on the amount of heat generated only in the motor control device (inverter).
In the present invention, preferably, the second cooling system for cooling the motor control device comprises a water pump and a radiator secured to a suspension system of the vehicle.
According to the present invention, since the radiator forming the second cooling system is secured to the high-strength suspension system of the vehicle, there is no need to provide another mounting member for mounting the radiator.
In the present invention, preferably, the suspension system of the vehicle is a lateral rod brace.
According to the present invention, the radiator is mounted in the vicinity of one end of the lateral rod brace. This eliminates the need for a high-strength bracket for retaining the radiator, so that the bracket with a simple structure can be manufactured. Also, the radiator is mounted in the vicinity (vehicle-body side) of one end of the lateral rod brace, thereby decreasing the length of a pipe connecting the radiator with the water pump secured to the vehicle body.
In the present invention, preferably, a part of the radiator forming the second cooling system for cooling the motor control device is covered with a rear bumper, and the area covered with the rear bumper is larger than the area that is not covered.
According to the present invention, most of the radiator is covered with the rear bumper, thereby protecting the radiator from external factors (bouncing stones, external forces applied from the rear of the vehicle, or the like).
In the present invention, preferably, an opening is provided at a part of the rear bumper which covers the radiator, and is covered with a mesh.
According to the present invention, the opening is formed at a part of the rear bumper which covers the radiator, so that the performance of the radiator and the cooling performance of the entire system can be improved. Also, the opening is provided with the mesh so as to protect the radiator.